Aerodynamic Characteristics of Flow over Circular Cylinders with Patterned Surface

Abstract

Abstract-Flow over circular cylinders with patterned surfaces is investigated and discussed taking into consideration the well known characteristics of flows over rough and dimpled cylinders in this paper. Investigations were performed in a subsonic wind tunnel to observe the effect of hexagonal patterns on the flow of air at Reynolds numbers ranging from 3.14E+04 to 2.77E+05. The investigations revealed that a patterned cylinder with patterns pressed outwards (can be referred as hexagonal bumps) has a drag coefficient equal to 65% of the smooth one. Various flow visualization techniques including measurement of velocity profiles in the wake region and smoke flow visualization were employed to elucidate the effect and hence comprehend the reason of drag reduction. Besides that the investigation of vortex shedding frequencies determined by using hot wire anemometry suggested that they do not change significantly with the decrease in drag coefficient in contrast to the dimpled cylinders.

Control of flow around a circular cylinder using a patterned surface

“…Figure 1 shows the influence of surface roughness on drag coefficient in terms of roughness coefficient k/D, where k is the average grain size of sand and D is the diameter of the circular cylinder [1,2]. It is also known that the drag characteristics are influenced by the surface figures, such as dimpled surfaces or grooved surfaces [3][4][5]. However, little studies have been carried out on the flow around a circular cylinder with partially patterned surface.…”

“…In this paper, drag coefficient of a circular cylinder having discretely patterned surface was compared with uniformly roughened surface. Effect of patterns were investigated in the wind tunnel test, changing arrangement shape and location of the indented patterns, up to the Reynolds number 5×10 5 . The behaviour of the discretely patterned surface of a circular cylinder is analysed by measuring drag coefficients and pressure distribution around cylinders.…”

Experimental study of heat transfer and hydraulic resistance at cross flow of tube bundle with indentations

“…In [4], cross flow over a cylinder with indentations and protrusions of a hexagonal shape in the Reynolds number range of 3.14•10 4 ...2.77•10 5 was investigated. Visualization showed that the separation displacement occurs at lower Reynolds numbers, in comparison with the critical Reynolds number on a smooth cylinder.…”

“…In [1][2][3][4][5], devoted to the cross flow of a single tube, the main emphasis is on the study of hydrodynamic regimes, the point of flow separation, the frequency of vortex shedding, the dependence of the drag resistance on the Reynolds number. In the works devoted to tube bundles, hydraulic losses, heat transfer and thermal and hydraulic efficiency were investigated.…”

“…Available publications [1][2][3][4][5][6][7][8] consider the cross flow of both a single tube and tube bundles with surface indentations in a wide range of Reynolds numbers. In [1][2][3][4][5], devoted to the cross flow of a single tube, the main emphasis is on the study of hydrodynamic regimes, the point of flow separation, the frequency of vortex shedding, the dependence of the drag resistance on the Reynolds number.…”